The present invention relates to a method and apparatus for actively controlling the gram load on a disk drive suspension assembly and a disk drive using the present disk drive suspension assembly.
Head suspension assemblies are commonly used in rigid magnetic disk drives to support magnetic heads in close proximity to the rotating disk surfaces. Head suspension assemblies of this type typically include an air bearing head slider assembly mounted to a suspension. The suspension includes a load beam having a mounting region on its proximal end and a gimbal or flexure on its distal end. When incorporated into a disk drive, the mounting region is mounted to an actuator or positioning arm, which supports the suspension assembly over the rotating disk. A baseplate is typically welded to the mounting region to increase the rigidity of the mounting region and to provide a mechanism for securely mounting the suspension assembly to the positioning arm.
The load beam is an elongated and often generally triangularly shaped member that includes a spring region adjacent to the mounting region, and a rigid region that extends from the spring region. The flexure can be manufactured as a separate member and welded to the distal end of the load beam, or formed as an integral member in the distal end of the load beam.
The air bearing head slider assembly contains a magnetic head and is typically bonded to the flexure by adhesive. The flexure allows the head slider assembly to move or xe2x80x9cgimbalxe2x80x9d(about rotational pitch and roll axes) with respect to the distal end of the load beam and thereby follow variations in the surface of the spinning disk. To enable the pivotal flexure movement, the surface of the flexure to which the head slider assembly is bonded is typically spaced from the adjacent surface of the load beam by structures known as load point dimples or formed offsets.
Suspensions are commonly manufactured by chemically etching flat or unformed load beam blanks from thin sheets of stainless steel. Flat and unformed flexure blanks are etched in a similar manner from sheets of stainless steel. During subsequent manufacturing operations, side rails, load point dimples and any other structures that extend upwardly or downwardly from the web or generally planar surface of the load beam are formed on the load beam blanks by mechanical bending procedures. Any dimples, offsets or other structures on the flexures requiring deformation of this type are formed in a similar manner. After forming, the flexures are welded to the distal end of the load beams. Baseplates are also welded to the suspensions following the forming operations.
The product of these etching, welding and forming operations are generally flat suspensions (i.e., the mounting region, spring region and rigid region of the load beam are generally coplanar and at the same height. During subsequent manufacturing operations, at least a portion of the spring region of the load beam is rolled around a curved mandrel or otherwise bent in such a manner as to plastically bend or permanently deform the spring region. The rolling operation imparts a curved shape to the spring region and causes the flexure to be offset from the mounting region when the suspension is in its unloaded or free state.
As noted above, the suspension supports the slider assembly over the magnetic disk. In one embodiment, air pressure at the surface of the spinning disk creates a positive pressure air bearing that causes the slider assembly to lift away from and xe2x80x9cflyxe2x80x9dover the disk surface. In another embodiment, a negative pressure air bearing pulls the slider assembly toward the disk surface. To counteract these hydrodynamic forces, the head suspension assembly is mounted to the disk drive with the suspension in a loaded state so the bent spring region of the suspension biases the head slider assembly either toward or away from the magnetic disk. The height at which the slider assembly flies over the disk surface is known as the xe2x80x9cfly height.xe2x80x9dThe force exerted by the suspension on the slider assembly when the slider assembly is at fly height is known as the xe2x80x9cgram load.xe2x80x9d
By controlling the gram load of the head suspension, the force applied to the read/write head at a constant flying level can be determined. Current suspensions have a gram load that is determined by a bend radius in the suspension arm. The accuracy of this type of gram loading method is typically about +/xe2x88x920.1 grams. Once bent into position, the suspension arm has no way of changing the gram load, unless subsequently bent or altered in a permanent way.
U.S. Pat. No. 5,898,541 (Boutaghou et al.) discloses a bi-morph piezoelectric bending motor mounted on the head slider. The bending motor cooperates with a tab surface on the flexure to rotate the slider.
U.S. Pat. No. 5,719,720 (Lee) discloses a load beam of a head suspension mechanism that has a non-load bearing, single layer of piezoelectric material on at least one surface of a resilient portion of the load beam. A controller apparatus provides a control signal to the piezoelectric material that induces expansion or contraction of the piezoelectric material to cause the load beam to raise the head slider from the surface in the disk drive. Since the piezoelectric material of the ""720 patent is limited to compression and expansion forces, it must be attached directly to the surface of the load beam. Consequently, the compression or expansion of the single layer piezoelectric material occurs along the length of the load beam and must overcome the stiffness of the load beam to produce a bending or curving motion of the resilient portion of the load beam. That is, the forces generated by the compression or expansion of the piezoelectric material are parallel to the surface of the load beam. Directing the forces from the piezoelectric material parallel to the load beam limits the amount of deflection and load applied to the load beam.
The present invention is directed to a method and apparatus for actively controlling the gram load on a disk drive suspension assembly and to a disk drive using the present head suspension. The gram load can be actively changed by changing the applied voltage to a multi-layer piezoelectric material attached to the head suspension. The active gram control system of the present invention allows the gram load to be changed on a non-permanent basis and to control the gram load to a much finer scale than can be accomplished using conventional techniques. The present active gram control system may also be used for active vibration damping, lifting the read/write head, a shock sensor, and for contact recording.
The present invention is directed to a disk drive suspension assembly that uses at least one piezoelectric actuator having two or more layers. In a two-layer embodiment, each layer of the multi-layer piezoelectric actuator is poled in such a fashion that when energized, one piezoelectric layer contracts while the other expands, resulting in a curling motion. In an embodiment with more than two layers, the piezoelectric actuator is poled to achieve a curling motion. By attaching the first and second ends of the piezoelectric actuator to discrete locations on the load beam, while the portion of the piezoelectric actuator between the first and second ends remains unattached to the load beam, a force that is non-parallel to the surface of the load beam can be applied to the head suspension. In one embodiment, the force is normal to the load beam.
In one embodiment, the load beam may include a compliant region located between the first and second attachment locations for the piezoelectric actuator. Consequently, the piezoelectric actuator in an unactuated state supports a portion of the gram load. By arranging the multi-layer piezoelectric to span across the compliant region, a greater range of motion and a greater range of gram loading can be achieved. Compliant region refers to a partial etch, a hole, a recess, a narrowing of the load beam, one or more lines of weakness extending generally laterally across load beam, or other features in the load beam that create a location of flexibility greater than elsewhere along the load beam.
The present invention is also directed to a disk drive using the present disk drive suspension assembly. The disk drive includes a rigid magnetic disk and a positioning arm attached to the actuator arm mounting region. The head mounting region on a distal end of the load beam includes at least one transducer head positioned opposite the rigid magnetic disk. The piezoelectric actuator has at least two layers. First and second ends of the piezoelectric actuator are attached to the load beam at first and second attachment locations, respectively, so that a force non-parallel to the load beam is applied to the head suspension in an actuated state. In one embodiment, the force is normal to the load beam.
The multi-layer piezoelectric actuator can be used to determine precisely the flying height of the read/write heads on the disk drive suspension. Moreover, the gram load can be changed with changing drive conditions. The multi-layer piezoelectric actuator can eliminate the need for an active head lifter and landing zones on the fixed disk, while protecting the read/write heads during periods of inactivity. Since the layers of the multi-layer act as both actuators and transducers, the various layers produce a voltage when deflected. In one embodiment, these voltages are extracted to dampen gram changing vibrations and deflections. In another embodiment, the extracted voltages can be actively counteracted to reduce gram changing vibrations.
The present invention is also directed to a method of making a disk drive suspension assembly in accordance with the present invention. A load beam is formed having a distal end, an actuator arm mounting region on a proximal end, a rigid region, and a spring region between the rigid region and actuator arm mounting region. A compliant region is formed in the load beam. A head mounting region is formed on a distal end of the load beam for receiving a transducer head. A piezoelectric actuator having at least two layers is assembled. First and second ends of the piezoelectric actuator are attached to first and second attachment locations on opposite sides of the compliant region of the load beam so that the piezoelectric actuator supports a portion of the gram load in an unactivated state. The method may include the step of applying a voltage to one at least one of the piezoelectric actuators to perform one or more of controlling the flying height of the head mounting region, modifying the gram load, raising or lowering the head mounting region, measuring vibrations and deflections of the load beam, dampening vibrations of the load beam, controlling attitude of the head mounting region, and applying a lateral force on the load beam.